Our celebrated countryman Roger Bacon, appears to have devoted a great share of his attcntion to the sub ject of optics. But though he studied the works of Al hazen, and of the other Arabian authors, he does not seem to have added any thing very important to the science. In his Perapectiva and his Specula Mathenzatica, he has treated lat gel) of optical subjects ; but these are only detached portions of his Opus Illajus, which contains an account of all his inventions and views. In this work he describes, in the clearest manner, the magnifying effects oduced by the use of convex lenses; and if he was unacquainted with spectacles and telescopes, he has certainly anticipate(' their invention in language more than prophetic. Wood, in his History of Oxford, Jebb, the editor of Opus Majua, and Alolyneux, in his Dioptrics, have all concurred in regarding Bacon as the inventor of the telescope ; and though we consider the question as not unattended with dIffieulties, wc cannot but be convinced that many an invention has been awarded on much less obscure pounds than those upon it, hich the telescope and microscope are given to Roger Bacon.
The following is a translation of the whole passage respecting convex lenses, which obviously describes the single microscope and spectacles.
4, If the letters of a book, or any minute object, be viewed through a lesser segment of a sphere of glass or crystal, whose plane base is laid upon them, they will appear far better and larger. Because, by. the fifth canon about a spherical medium whose convexity is to wards the eye, abd tile object is placed below it, and between the contexity and its centre, all things con cur to magnify it. For the angle under which it is seen is greater, and its image is also greater and nearer to the eye than the object itself, because the object is between the centre and the eye ; and therefore this instrument is useful to old mcn, and to those that have weak eyes ; for they may see the smallest letters suffi ciently magnified. But if the medium be the larger segment of a sphere, or but half of one, then, by the sixth canon, the apparent visual angle will be greater than the true, and the image also greater than the object ; but the place or it will be beyond the objcct, because the centre of the sphere is between the eye and the object ; and, therefore, this instrument is not so powerful in magnifying as a lesser segment of a sphere. Also in struments made of crystal bodies with plane surfaces, by the first canon about planes, and with concave sur faces, by the lirst and second canons about spherical sul laces, will perform the same thing. But the lesser of two segments of a sphere magnifies more manifestly than any of them all, by reason of the concurrence of all the three causes, as I said before." The passage which relates to the telescope and mi croscope is as follows : Greater things than these may be performed by re fracted vision. For it is easy to understand by thc canons above mentioned, that the greatest things may ap pear exceeding small, and on the contrary ; also that the most remote objects may appear just at hand, and on the contrary. For Ive can give such figures to transparent bodies, and dispose them in such order with respect to the eye and the objects, that (he rays shall be refracted and bent towards any place we please ; so that we shall see the object near at hand, or at a distance, under any angle we please. And thus from an incredible
distance we may read the smallest letters,and may num ber the smallest particles of dust and sand, by reason of the greatness of the angle under which We may see them ; and on the contrary, we may not be able to sec the greatest bodies just by us, by reason of the small ness of the angles under which they may appear ; for distance does not affect this kind or vision, excepting by accident, but the quantity of the angle. And thus a boy may appear to be a giant, and a man as big as a mountain, for as much as we may see the man under as great an angle as the mountain, and as near as we please ; and thus a small army may appear a very great one, and, though very far off, yet very near us, and on thc contrary. Thus also the sun, moon, and stars, may be made to descend hither in appearance, and to ap pear over the heads of our enemies ; and many things of the like sort, which would astonish unskilful per sons." It is scarcely possible to read this passage, and en tertain the sober conviction that Bacon had never put his speculations to the test of experiment. lie speaks, in deed, with all the conviction of actual trial, and should it be found that what he says is mere speculation, WC MUSt still entertain the opinion, that he was the first person who actually believed, and published his belief, that small objects could be magnified, and distant objects brought near, by means of single lenses, and combinations of lenses, and that these effects were produced by en larging by means of refraction the visual angles under which these objects were seen. Dr. Smith has en deavoured to repel the arguments in favour of Bacon being the inventor of the telescope, by pointing out the errors and inconsistencies of Ins sveculations; but there are many instances in the history or science, where in. ventions have been made by persons who knew little or nothing of the very principles upon which they were founded. That Bacon magnified objects with his lesser sphere, or a convex lens, is indubitable ; and when we consider that a single lens, or a single concave mirror, held at a distance from the eye, constitutes in reolitv a telescope, the eye performing the functions of an eye glass, we can scarcely. doubt that Bacon invented at !east a telescope of this description, If the invention of spectacles and of telescopes was not made by Roger Bacon, hc at least prepared the way for their immediate introduction. It seems quite certain, that spectacles were well known about the time of Bacon's death. Alexander Spina, of Pisa, who died in 1313, and who happened to see a pair of spectacles in the possession of another person, immediately con structed a pair for himself; and Muschenbroek informs us, that it is inscribed on the tomb of Salvinus Armatus, a nobleman of Florence, who died in 1317, that he was the inventor of spectacles.